Portion of a shoe midsole



FIG. 1 is a front perspective view of a portion of a shoe midsole showing my new design;

FIG. 2 is a rear perspective view thereof; and,

FIG. 3 is a side view thereof.

The broken lines immediately adjacent to the shaded area represents an unclaimed boundary of the design. The broken line showing of the remainder of the shoe is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a portion of a shoe midsole, as shown and described. 